What is the pH of a 0.00200 M HClO₄solution?

Question

Quizplus · Accepted Answer

HClO is a weak acid which dissociates partially in water, so we can use the equation Ka = [H+][ClO-]/[HClO] to find the pH of the solution. The Ka value for HClO is 3.5 × 10^-8. Since the concentration of HClO is very small compared to the minimum concentration required to change the pH significantly, we can neglect its contribution to the [H+] concentration. Therefore, [H+] ≈ [ClO-] = x (where x is the concentration of the HClO dissociation product). Thus, we can simplify the expression to Ka = x^2/[HClO] and solve for x: x = sqrt(Ka*[HClO]). Plugging in the given values we get x = 1.35 x 10^-3 M, and then we can calculate the pH using the expression pH = -log([H+]) = -log(x) = 2.699. Therefore, the correct answer is C.

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